At present, for formwork and dismantling formwork of building free-standing or load-bearing walls, boards (French Patent Disclosure A 1.277,437) are generally used, each including a shuttering face formed by one of the faces of a plate which is provided on its opposite face with reinforcements disposed along directions perpendicular to one another, in order by its rigidity to guarantee the geometric correction of the shuttered wall.
The shuttering face generally has a height substantially equal to the height of the wall to be poured, and a width as great as possible while remaining sufficiently slight to limit the weight of the board and as a result, for each face of the wall to be shuttered, use is generally made of a plurality of boards disposed longwise of one another and assembled together by means that assure continuity of the shuttering face.
Accordingly, these boards have their shuttering faces placed vertically facing one another, and they are braced against one another with a spacing between them corresponding to the thickness of the wall.
On at least one of their ends, they are provided with closure panels that shutter the vertical edges of the walls, or at least assure that the poured material will not escape at the sides.
To guarantee the verticality of their shuttering faces, these boards are associated, by their stiffeners, with a structure that affords the board at least one point of possibly adjustable support on the reference surface, at a certain distance from the shuttering face.
In the case where the free-standing or load-bearing walls are poured separately from horizontal walls joining the upper edges of two successive walls, the structure is generally formed by triangular trusses provided at a suitable distance with a support on the reference surface (French Patent Disclosure A 1,277,437).
In the most general case, where contrarily it is desirable, simultaneously with the vertical walls, to pour the horizontal wall that extends between the upper edges of those successive vertical walls, such as the ceiling slab of two free-standing or load-bearing walls of the same cubicle as a part of a building, the boards are disposed vertically with their stiffened faces facing one another, with a spacing between them corresponding to the distance between the vertical walls of the same cubicle and joined to one another:
first, in their upper part, by flooring in one or more parts, having a shuttering face, formed by the upper face of a plate whose lower face cooperates with stiffeners disposed in two directions perpendicular to one another, to guarantee the geometric correction of the wall, and PA1 second, by adjustable crossbeams near their base. PA1 for the formwork: PA1 for dismantling the formwork:
In this case, each board thus associated with the other board directly makes the structure that affords the other board the support point guaranteeing its verticality.
The associated vertical and horizontal shuttering faces lend the entire formwork apparatus the shape of an inverted U, commonly called a tunnel.
As for the flooring or at least one of its parts, it is known to associate it with a support structure on the reference surface that lends it the form of a table (French Patent Disclosure A 1,345,570).
It is also known to make the shuttering part of the board inseparable from the shuttering face of at least one part of the flooring.
In one known embodiment (French Patent Disclosure A 1.180,699), the flooring, properly stiffened by itself in two perpendicular directions, is cut into at least two lengths that are rejoined along the planes of joints parallel to the boards, and each length of flooring adjoins a board by its shuttering face associated with that of the board and by its transverse stiffeners articulated to the vertical stiffeners of the boards, so that the parts, generally called half-shells, of the tunnel-like formwork apparatus can be dismantled by deforming the dihedral angle between the length of flooring and the board.
In another known embodiment (French Patent Disclosure A 1.512.440), the flooring is not stiffened, at least locally, by itself except in a direction parallel to the boards, and at the time the formwork is done, in order to have the requisite evenness, it rests freely on crossbeams associated with the stiffeners of the boards.
To permit dismantling of the formwork, these support crossbeams of the flooring are each constituted by at least two profile sections articulated on the one hand to one another under the middle part of the flooring and on the other, by one of their ends, to the stiffeners of one of the boards.
The profile sections of these crossbeams, commonly known as scissors, can be maneuvered so as to form an angle between them that turns its concave side toward the flooring, thus at least locally depriving the flooring of its transverse stiffeners, so that by its own weight or by traction it can sag and thus assure dismantling of the horizontal wall, but also of the top of the vertical walls, by inclination of a few degrees, because of the reduction in the spacing that the maneuvering of the scissors induces in the upper portion of the tunnel.
In these two tunnel-type embodiments, and it is understood for pouring horizontal walls, such as closure panels provided on the boards, the flooring elements are equipped on their edges with slab-type stop panels, whose height is at least equal to the thickness of these horizontal walls, to prevent the poured material from escaping at the sides.
Regardless of the type of board used to finish off the dismantling of the formwork, its base is also, in a second period of time, disengaged from the wall by action on the structure provided on the back of the boards.
Although by itself the reference surface allows correct positioning of the boards both in height and in verticality, it does not allow determining the position of the base of the shuttering face of the board in the plane of this reference surface.
For that purpose, benchmarks provided with vertical faces rising to a low height are provided on the reference surface, each defining the position of the plane of one face of the wall to be erected, and against which the basis of the shuttering faces of the boards can then be made to abut.
To facilitate handling of these boards and the structures with which they are associated, the boards are currently equipped with wheels on their base that each rotate generally freely about an axis perpendicular to the shuttering face and supported by a cover attached directly to the back face of the shuttering plate, at a height such that the lower part of each wheel is located at a lower level than the lower edge of the shuttering face when the shuttering face is at least substantially vertical.
The lower edge of the shuttering face of the board can thus, with play and hence without friction on the reference surface, enable displacement of the board in a direction parallel to itself.
Since being supported by the wheels on the reference surface does not guarantee a definitive position of the board in its plane nor its immobilization, so that correct support is given to the boards in the formwork process, their wheels must be disengaged from the reference surface, and to that end, jacks are provided on the base of the boards, with a vertical axis and the lower end of which is provided with a runner for support on the reference surface.
Thus in the embodiments known at the present time, for pouring, the lower edge of the shuttering faces of the boards is always raised by the initial play increased by the height of disengagements of the wheels from the reference surface.
The corresponding interstice necessitates the provision, on the reference surface and/or on the boards, of means with a view to preventing the poured material from being capable of escaping.
To that end, it is known to provide a removable panel on the base of the boards for closure of the aforementioned interstice, but this panel, commonly known as an underlay block, and its means for articulation to the board make the board more complicated and require that additional maneuvering be done on the building site, which has a deleterious effect on the cost.
Another known solution consists in making positioning stops on the reference surface, which extend over the entire length of the boards and thus form footings of free-standing or load-bearing walls.
To make these footings at the same time as the walls and the ceiling slab on the lower level, it is necessary to provide not only the means associated with the boards on the lower level but also formwork angles for the footing and means for flanging them in the required position, which also increases the cost of the building site equipment and the cost for construction.
Moreover, the support of the shuttering face of the board on such a footing is never perfect, and hence defects in surface evenness appear on the formwork wall.